Photochromism is a phenomenon which has been known for many years. A compound is said to be photochromic when, after irradiation with a beam of light, certain wavelengths of which are in the ultraviolet region, this compound changes color and returns to its original color as soon as the irradiation ceases.
There are many applications of this phenomenon, but one of the more particularly advantageous known applications relates to the ophthalmic optics field.
Such compounds can be used in the manufacture of lenses or spectacle lens glasses for the purpose of screening light radiation as a function of its intensity.
The incorporation of photochromic compounds into an organic material constituting an ophthalmic lens makes it possible to obtain a lens glass whose weight is considerably reduced when compared with conventional lenses made of inorganic glass, which contain silver halides as photochromic agents. Their incorporation into organic materials has always posed technical difficulties.
However, any compound with photochromic properties cannot necessarily be used in the ophthalmic optics field. The reason for this is that the photochromic compound must satisfy a certain number of criteria, including, inter alia:
a high colorability, which is a measurement of the capacity of a photochromic compound to have an intense color after isomerization; PA1 a coloration after light absorption making the photochromic compound suitable, alone or in combination with other photochromic compounds to be used in ophthalmic glasses or lenses; PA1 an absence of coloration or very weak coloration in the initial form; PA1 rapid coloration or decoloration kinetics; PA1 a photochromism which manifests itself over the widest possible temperature range, and in particular preferably between 0 and 40.degree. C. PA1 i) an alkyl group of 1 to 16 carbon atoms such as a methyl, ethyl, n-propyl, isopropyl or n-butyl group; PA1 ii) an allyl group, a phenyl group, an arylalkyl group such as a benzyl group, a phenyl group mono- or disubstituted with substituents of the alkyl or alkoxy type of 1 to 6 carbon atoms or halogen atoms such as chlorine; PA1 iii) an alicyclic group such as an optionally substituted cyclohexyl group, PA1 iv) an aliphatic hydrocarbon group containing one or more hetero atoms such as O, N or S in its chain, in particular an acid, ester or alcohol function; PA1 i) a hydrogen atom, an amine function NR'R", where R' and R" each independently represent a hydrogen atom, an alkyl, cycloalkyl or phenyl group or a substituted derivative thereof; R' and R" may combine to form a cycloalkyl which may be substituted and may contain one or more hetero atoms; PA1 ii) a group R, OR, SR, COR or COOR, in which R represents a hydrogen atom, an alkyl group of 1 to 6 carbon atoms or an aryl or heteroaryl group; PA1 iii) a halogen atom, a C.sub.1 -C.sub.4 monohaloalkyl group, the halogen being Cl or Br in particular, or a C.sub.1 -C.sub.4 polyhaloalkyl group such as CF.sub.3 ; PA1 iv) --NO.sub.2, CN, SCN; PA1 v) a group ##STR2## with R.sub.8 representing H or CH.sub.3 ; vi) a group ##STR3## it being possible for each of the substituents R.sub.4 to be present on any of the suitable carbon atoms of the indoline part of the photochromic compound, in positions 4, 5, 6 and 7, when the other is a hydrogen atom, whereas, when n=2, it is preferably for the substituents to be present in positions 4 and 5, 5 and 6, 4 and 6 or 6 and 7; PA1 R.sub.2 and R.sub.3 represent, independently of each other, an alkyl group having from 1 to 8 carbon atoms; PA1 R.sub.4 denotes a halogen atom, a hydrogen atom or an alkoxy radical having from 1 to 6 carbon atoms, a group ##STR6## with R.sub.8 denoting H or CH.sub.3, or a group ##STR7## R.sub.6 has the meaning mentioned above in formula (I). PA1 R.sub.2 denotes an alkyl having from 1 to 8 carbon atoms; PA1 R.sub.4 denotes a halogen atom, a hydrogen atom, an alkoxy radical having from 1 to 6 carbon atoms or a radical ##STR10## with R.sub.8 denoting H or CH.sub.3. PA1 R.sub.1 preferably denotes a methyl, hexadecyl or allyl radical; PA1 R.sub.2 preferably denotes a methyl or ethyl radical; PA1 R.sub.4 preferably denotes a hydrogen, chlorine, a methoxy radical or the radical ##STR11##
The known and currently used organic photochromic compounds generally have a decreasing photochromism when the temperature increases, such that the photochromism is particularly pronounced at temperatures close to 0.degree. C., whereas it is much weaker, or even nonexistent, at temperatures of about 40.degree. C., these being temperatures which lens glasses may reach, in particular during exposure to the sun.
Another problem encountered for the photochromic compounds of the prior art is their lifetime. Indeed, for certain products of the prior art, a relatively short lifetime is observed. The reason for this is that after a certain number of coloration and decoloration cycles, the compound no longer has reversible photochromic properties.
The photochromic properties of spiroxazines have been described by R. E. Fox in the document Final Report of Contact AF 41, A.D. 440226 1961. 657.
Compounds of the spiro (indoline-naphthoxazine) type have been synthesized and described in particular in the article by N. Y. C. Chu "Photochromism: Molecules and Systems" Ed. H. Durr, H. Bovas Laurent, Elsevier, Amsterdam 1990, ch. 24, as well as compounds of the spiro(indoline-quinazolinoxazine) or spiro(indoline-benzothiazoloxazine) type in U.S. Pat. Nos. 5,139,707 and 5,114,621 (R. Guglielmetti, P. Tardieu) granted in the name of the company Essilor.
Compounds of the photochromic spiroindoline-2,3'!benzoxazine! type have also been synthesized and described in patent application EP-0,245,020.
Japanese patent application JP 3,251,587 moreover discloses photochromic compounds of the indolinospiropyridobenzoxazine type bearing, in the 6' position of the benzoxazine nucleus, CN, CF.sub.3 or alkoxycarbonyl groups, and the indoline nitrogen of which is substituted with alkoxycarbonylalkyl groups.
These compounds are photochromic at temperatures of about from 30 to 40.degree. C.
These compounds, in their open form, have an absorption spectrum in the visible region containing an absorption maximum at a wavelength .lambda..sub.max ranging from 600 to 617 nm.
It is desirable to obtain compounds whose absorption spectrum in the visible region, for their open form, contains an absorption maximum at wavelengths higher than those of the compounds of patent application JP 3,251,587.
Indeed, shifting of the .lambda..sub.max value to higher values leads to photochromic compounds of color approaching green in their open form, this color being desired for ophthalmic use.